1. Field of the Invention
This invention relates to a disc brake used for braking an automobile and more particularly to construction of the disc brake for the prevention of noise in braking.
2. Description of the Prior Art
As shown in FIGS. 1 and 5, the disc brake is arranged so that a pair of inner and outer pads 3 are slidably mounted to hold a disc rotor 1 therebetween in the Z direction of the axle (rotor shaft) on a support 2 which is provided to hold therebetween the circumference of the rotor. The rotor is connected to a wheel for rotation thereof, the support 2 having mounted thereon a caliper 4 which is adapted for slidable movement in the Z direction of the axle and which is provided with caliper pawls 4a, 4a.
For braking, one pad (inner pad) is urged against one side of the rotor 1 and, by use of the caliper 4, is allowed to slide on the support 2 under reaction against the compressive force. The other pad (outer pad) is pressed against the other side of the rotor 1 by the caliper pawls 4a, 4a, thereby firmly clamping the rotor from the opposite sides thereof to effect braking.
Such disc brakes functioning in the aforementioned manner often generate a noise, thus giving passengers and pedestrians an unpleasant feeling.
Various devices have been proposed heretofore for prevention of the noise. Some of them have been adapted to dispose between the pads, piston, and the pawls a shim plate formed of sheet steel coated with rubber on one side thereof to reduce the noise. For this reason, this type of device has been widely employed.
What have been above proposed are, however, efficacious to reduce noise of more than about 5 KHz (hereinafter referred to as "first noise") but are not efficacious to reduce second noise of less than about 4-1.7 KHz (hereinafter referred to as "squeal"). The unpreventable squeal is not always produced in every model of a car but tends to be permanently generated once it does appear and is much noisier than the first noise. There have been instances in which a small-sized disc brake for a light car produces as loud a noise as a disc brake on a large truck.
FIG. 2 is a graph showing a frequency analysis of loudness of squeal wherein 5 designates a fundamental wave, and 6, 7 denote harmonics, 8 being background noise.
FIG. 3 is a graph showing a frequency analysis of loudness of the first noise wherein 9 indicates a fundamental wave of 6.2 KHz.
What will be listed hereinafter has been found by the aforementioned measurement of squeal.
(1) Amplitude of vibration is shown as the highest in the pad out of the important components (i.e., components such as the caliper, pad, support and the rotor) but amplitude is too low in the others to take up.
(2) Amplitude is also shown as the highest in the Z direction of the pad, out of the directions X, Y and Z shown in FIG. 4.
(3) FIG. 4 shows direction of amplitude at the moment when squeal is generated, as well as magnitude of amplitude, wherein the opposite ends of the pad are the positions where an antinode of amplitude occurs in the Z direction and the center is the position where a node occurs.
It has been observed from what is aforementioned that the conventional disc brake is not so fabricated that amplitude of the opposite ends of the pad, depicted as where the antinode occurs when the squeal is produced, is efficiently lowered. In other words, the position where the pad is held by the caliper pawls is inside the end of the pad. Further, the surfaces of the caliper pawls which abut against the pad are finished by cutting and machining to a higher tolerance. In general, the back metal on the pad set against such surfaces is simply punched out of blank such as a steel plate. The back metal 3a does not uniformly contact the pawl 4a to render amplitude damping action unstable whereby a squeal is readily generated.
Japanese Utility Model Public Disclosures Nos. 160433/82 and 181939/82 are intended to prevent the disc brake from generating squeal and designed to have the caliper pawls hold in the neighborhood of a portion of the pad at which a node occurs, thereby lowering the sound. This is entirely different from the present invention which is adapted to hold the ends of the pad to be the position at which the antinode occurs.